A neurologist is a physician who diagnoses and treats disorders of the nervous system which is comprised of the brain, spinal cord and nerves. These doctors do not perform surgery, but refer patients to neurological surgeons when they determine that surgical intervention is necessary.
Some of the conditions that neurologists diagnose and treat are epilepsy, aneurysms, hydrocephalus, Parkinson's disease, multiple sclerosis, stroke, spinal disc herniation, and spinal disease.
In addition to using diagnostic tests like MRI, CT scans, EEG and EMG, neurologists also employ neurological testing to gauge muscle strength and movement, balance, reflexes, sensation, memory, speech, and other cognitive abilities.

Also sometimes referred to as intensivists, critical care specialists are physicians with specialized training in the diagnosis and management of life-threatening conditions. Some of these conditions affect vital organs like the heart and lungs, those that make breathing difficult or impossible, and those that affect entire organ systems, like the renal system.
Critical care specialists are typically found in a hospital's intensive care unit where they monitor patients with life-threatening conditions and make determinations as to the best course of treatment.

A dentist is a doctor who diagnoses and treats oral health issues. The most basic services dentists provide are preventative and regular maintenance treatments such as cleanings, fluoride treatments, X-rays (to look for cavities), cavity fillings. He or she also provides advice on proper brushing, flossing, and rinsing for the prevention of plaque buildup.

A pulmonologist is a physician who specializes in the diagnosis and treatment of conditions related to the lungs and respiratory tract.
These specialists are similar to critical care specialists in that their patients often require mechanical ventilation to assist their breathing.
Pulmonologists diagnose and treat patients with conditions such as asthma, cystic fibrosis, asbestosis, pulmonary fibrosis, lung cancer, COPD, and emphysema. Exposure and inhalation of certain toxic substances may also warrant the services of a pulmonologist.
Some of the tools and tests pulmonologists use to diagnose a patient are a stethoscope in order to listen for abnormal breathing sounds, chest X-rays, CT scans, blood tests, bronchoscopy, and polysomnography.

A sleep medicine specialist is specially trained in diagnosing and treating disorders involving sleep.
Sleep disorders such as sleep apnea, restless leg syndrome and insomnia are very common and can often cause other serious health issues, such as depression, asthma, and migraines. Sleep medicine specialists often work in sleep centers where they observe a patient while sleeping and monitor brain waves, behavior, and vital signs in order to identify the causes of sleep disturbance, or an inability to sleep (insomnia).
Sleep medicine specialists treat patients through advising on sleep hygiene, providing cognitive behavioral therapy, using light therapy, or medical sleep aides.

A psychiatrist is a doctor with specific training in the diagnosis and treatment of mental illness.
He or she can not only provide the counseling necessary to both diagnose and treat a patient, but can also prescribe medication when needed. In some cases, a psychiatrist will only provide the medication and the counseling will be provided by another healthcare specialist, like a certified counselor or psychologist.
Like other doctors, psychiatrists employ diagnostic tools like CT scans and MRI in order to observe the structure and function of a patient's brain.
Once a diagnosis is made, these specialists may use behavior or cognitive therapy in order to address the patient's condition, or a multitude of other types of therapy, in conjunction with or in place of medication.